Mixing is a process in which two or more substances are combined while the chemical properties of each substance remain largely unchanged. The properties of the overall mixture, however, can differ from those of the component substances. Thus, mixing is often used to produce a medium with a desired set of physical and chemical properties which can be confirmed by analytical techniques.
For example, in semiconductor fabrication, chemical mechanical planarization/polishing (CMP) is used to make wafer surfaces flat. This process requires use of a slurry containing abrasive particles dispersed in a liquid chemical composition (such as those containing an acid and/or a base). The CMP slurry is typically manufactured by mixing various chemicals and abrasive particles to form a dispersion (e.g., a colloidal dispersion). During CMP, movement of the abrasive particles on the wafer mechanically removes material from the wafer surface. The acid or base in the slurry facilitates the chemical removal of material by reacting with the material to be removed. Hence, the process is called “chemical” “mechanical” polishing. To produce CMP slurries having desired properties, it can be useful to filter the CMP slurries to achieve the desired distribution of abrasive particles dispersed within the chemically reactive agents. The filtration also ensures that the end CMP product has high purity.
As the semiconductor wafers become more advanced, the features on the wafer surfaces become finer and more complex. Planarizing these complex fine features requires very tight polish processing windows. Hence the CMP process requires that the CMP slurry property specifications are very tight. This, in turn, is forcing the CMP slurry manufacturers to significantly improve their production process capability while reducing variations between lots. The conventional slurry production processes are unable to meet these stringent demands.
Conventional slurry manufacturing processes include a Batch process (FIG. 2) and a Continuous Process (FIG. 3). In a batch process, all the slurry components are added to a large tank one by one (usually by a fluid transfer unit such as a pump, and/or a flow controller unit), followed by mixing the components by an agitator type device and a QC (quality control) step. After that, the mixed slurry is sent to packaging station usually through a filter station. The batch process suffers from many drawbacks including a large environmental footprint, long addition and mixing times, high property variations, low throughput, and high production costs.
A conventional continuous process (FIG. 3), on the other hand, replaces the very large tanks in the batch process with smaller tanks, and introduces in-line static or dynamic mixers. The raw materials are fed into these in-line mixers one by one (but never all together in one mixer). This design allows the process to be continuous and increases the throughput. However, the in-line mixers are small and create high back pressures. Each raw material flow component loop going to the in-line mixer creates flow control issues causing significant property variations. Thus, the continuous process cannot meet the tight specification demands either.
This disclosure describes an Advanced Continuous Process and related system that addresses these shortcomings.